1. Field of the Invention
This invention relates to the field of gas conversion and more specifically to the field of converting hydrogen sulfide to recover sulfur.
2. Background of the Invention
Processes for removing hydrogen sulfide from affluent gaseous and liquid streams and converting hydrogen sulfide into elemental sulfur have been widely used. For instance, chemical and electrochemical processes have been used to recover sulfur. One example of a chemical process is the Claus process, which is typically used for large-scale production of sulfur from hydrogen sulfide gas in a two-step method. Drawbacks of the Claus process include the tail gas containing a significant amount of hydrogen sulfide and sulfur dioxide gases. Moreover, the process typically has to be built on a large scale to be economically feasible. Another chemical process is thermal decomposition, which involves directly decomposing hydrogen sulfide gas into sulfur and hydrogen gas at an elevated temperature. Problems with the thermal decomposition process include inefficiencies typically involved in separating between sulfur and hydrogen gas at high temperatures. An additional chemical process includes oxidizing the hydrogen sulfide into sulfur using chemical oxidizers such as transition metal oxides and iodine. Problems involve the consumption of oxidizers that can result in the sulfur containing a metal oxidizer, which may reduce its economic value.
Electrochemical processes include electrolysis in aqueous solutions and high temperature processes. In processes involving electrolysis in aqueous solutions, a cation-conductive membrane is typically used to prevent polysulfide ions from reaching a cathode and thereby being reduced back to sulfide ions. Drawbacks include the economic costs of the membrane as well as a high consumption of energy with the process. Processes involving high temperatures involve high temperature fuel cells that have a membrane typically comprising oxygen-conductive or proton-conductive oxide material. Problems with such high temperature processes include the resulting gases from the oxygen-conductive membrane containing sulfur dioxide, and the lack of stability in the membrane and electrode with proton-conductive membranes.
Consequently, there is a need for an economical process for removing sulfur from toxic gases such as hydrogen sulfide. Additional needs include an improved process for recovering sulfur in which the resulting gas is relatively clean of sulfur dioxide.